More than a day after industrial waste water leaked from a Suncor Energy Inc. site into the Athabasca River, the oil-sands giant and the province were still trying to determine which, if any, toxic materials were carried into the major Alberta waterway.

On Monday, staff at the Suncor oil-sands base plant north of Fort McMurray discovered a pipe carrying water that had been used in bitumen extraction and upgrading had frozen, cracked and was leaking into an outfall pond near the river for at least several hours. They were able to halt the flow at 4 p.m. the same day.

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Late on Tuesday, Suncor confirmed some of this industrial waste water flowed from the pond into the Athabasca River.

With a decision on the approval of the Keystone XL pipeline looming in the U.S.  and scrutiny of the environmental effects of the oil sands ramping up  the leak comes at a delicate time for Canadas energy industry.

Once it hit the approved discharge point, it was diluted with water that is intended for release and then flowed into the river, said Suncor spokeswoman Sneh Seetal.

Suncor doesnt yet know the amount of industrial waste water released  or its makeup  but Ms. Seetal said staff believe the industrial waste water was so diluted, the potential for harm is low.

We dont anticipate any impact on the river. But as a precautionary measure, we are continuing to analyze river samples downstream from the release, she said, noting an investigation will continue.

Although it is not clear exactly what was in the mix of the leaked industrial waste water  otherwise known as process-affected water  Suncor was unable to exclude the possibility it included tailings. Tailings are the leftovers of oil sands production, and can contain fine silts, unrecovered hydrocarbons, and materials including naphthenic acids, ammonia, and mercury  all toxic to aquatic organisms and mammals.

The leak comes during a week when Industry officials are touring an NBC TV crew around the Fort McMurray area, filming at various sites (but not Suncor) for a news story about the Keystone pipeline and the significance of the massive oil-sands reserves to the U.S.

Albertas Ministry of Environment and Sustainable Resource Development was notified by Suncor at 1:45 p.m. Monday afternoon that the valve was open and their process water was flowing, spokeswoman Jessica Potter said. At 2:30 p.m. Monday, Suncor said the water flow had been reduced to a trickle. By 4 p.m., the line had been completely shut down.

Ministry staff are now investigating and are also testing the river, and will decide whether any punishment is required.

Environment Minister Diana McQueen said the Redford government takes these types of incidents seriously, and even in the face of critics who say Albertas environmental laws arent robust enough, the quick response from both government and the company shows otherwise. Ive got to tell you, our team  as soon as they were notified  was there on the scene, Ms. McQueen said in an interview.

People living and working downstream of the plant, including native communities, were notified of the release on Monday afternoon as well.

But with many questions about the water leak still unanswered, Athabasca Chipewyan Chief Allan Adam  a long-standing opponent to oil-sands development being ramped up  said the Suncor industrial waste-water leak is one of the reasons he and other chiefs went to Ottawa last week to announce they would continue to oppose proposed pipeline projects to transport crude from Albertas oil sands.

It just goes to prove, accidents do happen, Chief Adam said on Tuesday.

Water-quality issues have become an increasing concern in Albertas oil-sands region. In January, a peer-reviewed study by a research team including Environment Canada scientists found levels of polycyclic aromatic hydrocarbons in lakes near the Athabasca oil sands have risen roughly at the same pace as development.